After just purchasing a 747-400 with a big reputation from the other company (you know who) I think FSX desperately needs a good one.
IMHO that model is badly done and I'm now sorry I bought it, the VC is a joke.

Since CS haven't done any next gen aircraft I thnk they should stick with their model and build a nice 747-100/200/300 with FE panels.

There are currently only 3 possibly 4 long range aircraft around, those being Airbus A340-500/600 and you could probably throw the A330 in as well and Boeing have the 777 and 747.EDIT: Oops I forgot the elephant in the room the A380 but that doesn't interest me.
Going by Captain Sims past efforts the newer aircraft won't be done i.e A330/340 and the 777 so that leaves us with one LR aircraft to be done.

We already have the 727 and 757 for short range, mid range is covered by the 767 and upcoming 707, so it's about time for the extra legs.  :)

The only other aircraft I really want would be an early Airbus either A300 or 310. Preferably the 300 with FE panels. But I think we need something genuinely long range first.